libavcodec/ac3dec.c File Reference

#include <stdio.h>
#include <stddef.h>
#include <math.h>
#include <string.h>
#include "libavutil/crc.h"
#include "libavutil/opt.h"
#include "internal.h"
#include "aac_ac3_parser.h"
#include "ac3_parser.h"
#include "ac3dec.h"
#include "ac3dec_data.h"
#include "kbdwin.h"

Go to the source code of this file.

Data Structures

struct  mant_groups
 Grouped mantissas for 3-level 5-level and 11-level quantization. More...

Defines

#define OFFSET(x)   offsetof(AC3DecodeContext, x)
#define PAR   (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)

Functions

static int symmetric_dequant (int code, int levels)
 Symmetrical Dequantization reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization Tables 7.19 to 7.23.
static av_cold void ac3_tables_init (void)
static av_cold int ac3_decode_init (AVCodecContext *avctx)
 AVCodec initialization.
static int ac3_parse_header (AC3DecodeContext *s)
 Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.
static int parse_frame_header (AC3DecodeContext *s)
 Common function to parse AC-3 or E-AC-3 frame header.
static void set_downmix_coeffs (AC3DecodeContext *s)
 Set stereo downmixing coefficients based on frame header info.
static int decode_exponents (GetBitContext *gbc, int exp_strategy, int ngrps, uint8_t absexp, int8_t *dexps)
 Decode the grouped exponents according to exponent strategy.
static void calc_transform_coeffs_cpl (AC3DecodeContext *s)
 Generate transform coefficients for each coupled channel in the coupling range using the coupling coefficients and coupling coordinates.
static void ac3_decode_transform_coeffs_ch (AC3DecodeContext *s, int ch_index, mant_groups *m)
 Decode the transform coefficients for a particular channel reference: Section 7.3 Quantization and Decoding of Mantissas.
static void remove_dithering (AC3DecodeContext *s)
 Remove random dithering from coupling range coefficients with zero-bit mantissas for coupled channels which do not use dithering.
static void decode_transform_coeffs_ch (AC3DecodeContext *s, int blk, int ch, mant_groups *m)
static void decode_transform_coeffs (AC3DecodeContext *s, int blk)
 Decode the transform coefficients.
static void do_rematrixing (AC3DecodeContext *s)
 Stereo rematrixing.
static void do_imdct (AC3DecodeContext *s, int channels)
 Inverse MDCT Transform.
static void ac3_upmix_delay (AC3DecodeContext *s)
 Upmix delay samples from stereo to original channel layout.
static void decode_band_structure (GetBitContext *gbc, int blk, int eac3, int ecpl, int start_subband, int end_subband, const uint8_t *default_band_struct, int *num_bands, uint8_t *band_sizes)
 Decode band structure for coupling, spectral extension, or enhanced coupling.
static int decode_audio_block (AC3DecodeContext *s, int blk)
 Decode a single audio block from the AC-3 bitstream.
static int ac3_decode_frame (AVCodecContext *avctx, void *data, int *got_frame_ptr, AVPacket *avpkt)
 Decode a single AC-3 frame.
static av_cold int ac3_decode_end (AVCodecContext *avctx)
 Uninitialize the AC-3 decoder.

Variables

static uint8_t ungroup_3_in_7_bits_tab [128][3]
 table for ungrouping 3 values in 7 bits.
static int b1_mantissas [32][3]
 tables for ungrouping mantissas
static int b2_mantissas [128][3]
static int b3_mantissas [8]
static int b4_mantissas [128][2]
static int b5_mantissas [16]
static const uint8_t quantization_tab [16]
 Quantization table: levels for symmetric.
static float dynamic_range_tab [256]
 dynamic range table.
static const float gain_levels [9]
 Adjustments in dB gain.
static const uint8_t ac3_default_coeffs [8][5][2]
 Table for default stereo downmixing coefficients reference: Section 7.8.2 Downmixing Into Two Channels.
static const AVOption options []
static const AVClass ac3_decoder_class
AVCodec ff_ac3_decoder


Define Documentation

#define OFFSET (  )     offsetof(AC3DecodeContext, x)

Definition at line 1428 of file ac3dec.c.

#define PAR   (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)

Definition at line 1429 of file ac3dec.c.


Function Documentation

static av_cold int ac3_decode_end ( AVCodecContext avctx  )  [static]

Uninitialize the AC-3 decoder.

Definition at line 1419 of file ac3dec.c.

static int ac3_decode_frame ( AVCodecContext avctx,
void *  data,
int got_frame_ptr,
AVPacket avpkt 
) [static]

Decode a single AC-3 frame.

Definition at line 1265 of file ac3dec.c.

static av_cold int ac3_decode_init ( AVCodecContext avctx  )  [static]

AVCodec initialization.

Definition at line 160 of file ac3dec.c.

static void ac3_decode_transform_coeffs_ch ( AC3DecodeContext s,
int  ch_index,
mant_groups m 
) [static]

Decode the transform coefficients for a particular channel reference: Section 7.3 Quantization and Decoding of Mantissas.

Definition at line 428 of file ac3dec.c.

Referenced by decode_transform_coeffs_ch().

static int ac3_parse_header ( AC3DecodeContext s  )  [static]

Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.

GetBitContext within AC3DecodeContext must point to the start of the synchronized AC-3 bitstream.

Definition at line 203 of file ac3dec.c.

Referenced by parse_frame_header().

static av_cold void ac3_tables_init ( void   )  [static]

Definition at line 108 of file ac3dec.c.

Referenced by ac3_decode_init().

static void ac3_upmix_delay ( AC3DecodeContext s  )  [static]

Upmix delay samples from stereo to original channel layout.

Definition at line 626 of file ac3dec.c.

Referenced by decode_audio_block().

static void calc_transform_coeffs_cpl ( AC3DecodeContext s  )  [static]

Generate transform coefficients for each coupled channel in the coupling range using the coupling coefficients and coupling coordinates.

reference: Section 7.4.3 Coupling Coordinate Format

Definition at line 387 of file ac3dec.c.

Referenced by decode_transform_coeffs().

static int decode_audio_block ( AC3DecodeContext s,
int  blk 
) [static]

Decode a single audio block from the AC-3 bitstream.

Definition at line 719 of file ac3dec.c.

Referenced by ac3_decode_frame().

static void decode_band_structure ( GetBitContext gbc,
int  blk,
int  eac3,
int  ecpl,
int  start_subband,
int  end_subband,
const uint8_t default_band_struct,
int num_bands,
uint8_t band_sizes 
) [static]

Decode band structure for coupling, spectral extension, or enhanced coupling.

The band structure defines how many subbands are in each band. For each subband in the range, 1 means it is combined with the previous band, and 0 means that it starts a new band.

Parameters:
[in] gbc bit reader context
[in] blk block number
[in] eac3 flag to indicate E-AC-3
[in] ecpl flag to indicate enhanced coupling
[in] start_subband subband number for start of range
[in] end_subband subband number for end of range
[in] default_band_struct default band structure table
[out] num_bands number of bands (optionally NULL)
[out] band_sizes array containing the number of bins in each band (optionally NULL)

Definition at line 667 of file ac3dec.c.

Referenced by decode_audio_block().

static int decode_exponents ( GetBitContext gbc,
int  exp_strategy,
int  ngrps,
uint8_t  absexp,
int8_t *  dexps 
) [static]

Decode the grouped exponents according to exponent strategy.

reference: Section 7.1.3 Exponent Decoding

Definition at line 350 of file ac3dec.c.

Referenced by decode_audio_block().

static void decode_transform_coeffs ( AC3DecodeContext s,
int  blk 
) [static]

Decode the transform coefficients.

Definition at line 538 of file ac3dec.c.

Referenced by decode_audio_block().

static void decode_transform_coeffs_ch ( AC3DecodeContext s,
int  blk,
int  ch,
mant_groups m 
) [static]

Definition at line 518 of file ac3dec.c.

Referenced by decode_transform_coeffs().

static void do_imdct ( AC3DecodeContext s,
int  channels 
) [inline, static]

Inverse MDCT Transform.

Convert frequency domain coefficients to time-domain audio samples. reference: Section 7.9.4 Transformation Equations

Definition at line 598 of file ac3dec.c.

Referenced by decode_audio_block().

static void do_rematrixing ( AC3DecodeContext s  )  [static]

Stereo rematrixing.

reference: Section 7.5.4 Rematrixing : Decoding Technique

Definition at line 574 of file ac3dec.c.

Referenced by decode_audio_block().

static int parse_frame_header ( AC3DecodeContext s  )  [static]

Common function to parse AC-3 or E-AC-3 frame header.

Definition at line 243 of file ac3dec.c.

Referenced by ac3_decode_frame().

static void remove_dithering ( AC3DecodeContext s  )  [static]

Remove random dithering from coupling range coefficients with zero-bit mantissas for coupled channels which do not use dithering.

reference: Section 7.3.4 Dither for Zero Bit Mantissas (bap=0)

Definition at line 505 of file ac3dec.c.

Referenced by decode_transform_coeffs().

static void set_downmix_coeffs ( AC3DecodeContext s  )  [static]

Set stereo downmixing coefficients based on frame header info.

reference: Section 7.8.2 Downmixing Into Two Channels

Definition at line 303 of file ac3dec.c.

Referenced by ac3_decode_frame().

static int symmetric_dequant ( int  code,
int  levels 
) [inline, static]

Symmetrical Dequantization reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization Tables 7.19 to 7.23.

Definition at line 100 of file ac3dec.c.

Referenced by ac3_tables_init().


Variable Documentation

const AVClass ac3_decoder_class [static]

Initial value:

 {
    .class_name = "AC3 decoder",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
}

Definition at line 1442 of file ac3dec.c.

const uint8_t ac3_default_coeffs[8][5][2] [static]

Initial value:

 {
    { { 2, 7 }, { 7, 2 },                               },
    { { 4, 4 },                                         },
    { { 2, 7 }, { 7, 2 },                               },
    { { 2, 7 }, { 5, 5 }, { 7, 2 },                     },
    { { 2, 7 }, { 7, 2 }, { 6, 6 },                     },
    { { 2, 7 }, { 5, 5 }, { 7, 2 }, { 8, 8 },           },
    { { 2, 7 }, { 7, 2 }, { 6, 7 }, { 7, 6 },           },
    { { 2, 7 }, { 5, 5 }, { 7, 2 }, { 6, 7 }, { 7, 6 }, },
}
Table for default stereo downmixing coefficients reference: Section 7.8.2 Downmixing Into Two Channels.

Definition at line 83 of file ac3dec.c.

Referenced by set_downmix_coeffs().

int b1_mantissas[32][3] [static]

tables for ungrouping mantissas

Definition at line 48 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b2_mantissas[128][3] [static]

Definition at line 49 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b3_mantissas[8] [static]

Definition at line 50 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b4_mantissas[128][2] [static]

Definition at line 51 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

int b5_mantissas[16] [static]

Definition at line 52 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch(), and ac3_tables_init().

float dynamic_range_tab[256] [static]

dynamic range table.

converts codes to scale factors.

Definition at line 64 of file ac3dec.c.

Referenced by ac3_tables_init(), and decode_audio_block().

Initial value:

 {
    .name           = "ac3",
    .type           = AVMEDIA_TYPE_AUDIO,
    .id             = AV_CODEC_ID_AC3,
    .priv_data_size = sizeof (AC3DecodeContext),
    .init           = ac3_decode_init,
    .close          = ac3_decode_end,
    .decode         = ac3_decode_frame,
    .capabilities   = CODEC_CAP_DR1,
    .long_name      = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
    .sample_fmts    = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_FLT,
                                                      AV_SAMPLE_FMT_S16,
                                                      AV_SAMPLE_FMT_NONE },
    .priv_class     = &ac3_decoder_class,
}

Definition at line 1449 of file ac3dec.c.

const float gain_levels[9] [static]

const AVOption options[] [static]

Initial value:

 {
    { "drc_scale", "percentage of dynamic range compression to apply", OFFSET(drc_scale), AV_OPT_TYPE_FLOAT, {.dbl = 1.0}, 0.0, 1.0, PAR },

{"dmix_mode", "Preferred Stereo Downmix Mode", OFFSET(preferred_stereo_downmix), AV_OPT_TYPE_INT, {.i64 = -1 }, -1, 2, 0, "dmix_mode"},
{"ltrt_cmixlev",   "Lt/Rt Center Mix Level",   OFFSET(ltrt_center_mix_level),    AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"ltrt_surmixlev", "Lt/Rt Surround Mix Level", OFFSET(ltrt_surround_mix_level),  AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"loro_cmixlev",   "Lo/Ro Center Mix Level",   OFFSET(loro_center_mix_level),    AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"loro_surmixlev", "Lo/Ro Surround Mix Level", OFFSET(loro_surround_mix_level),  AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},

    { NULL},
}

Definition at line 1430 of file ac3dec.c.

const uint8_t quantization_tab[16] [static]

Initial value:

 {
    0, 3, 5, 7, 11, 15,
    5, 6, 7, 8, 9, 10, 11, 12, 14, 16
}
Quantization table: levels for symmetric.

bits for asymmetric. reference: Table 7.18 Mapping of bap to Quantizer

Definition at line 58 of file ac3dec.c.

Referenced by ac3_decode_transform_coeffs_ch().

uint8_t ungroup_3_in_7_bits_tab[128][3] [static]

table for ungrouping 3 values in 7 bits.

used for exponents and bap=2 mantissas

Definition at line 45 of file ac3dec.c.

Referenced by ac3_tables_init(), and decode_exponents().


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